Devices and techniques for anchoring an implantable medical device

ABSTRACT

Anchoring mechanisms for an implantable electrical medical lead that is positioned within a substernal space are disclosed. The anchoring mechanisms fixedly-position a distal portion of the lead, that is implanted in the substernal space.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority from U.S. ProvisionalApplication No. 61/820,024, filed on May 6, 2013, the content of whichis incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present application relates to implantable medical devices. Inparticular, methods, techniques devices are disclosed for anchoringimplantable medical leads.

BACKGROUND OF THE INVENTION

Electrical stimulation of body tissue and organs is often used as amethod of treating various conditions. Such stimulation is generallydelivered by means of electrical contact between a pulse generatordevice and a target site via one or more implantable medical electricalleads connected to the pulse generator device; implantable leadstypically include one or more stimulation electrodes joined to a distalportion of the lead, which are positioned and anchored in proximity tothe target site.

In patients at high risk of ventricular fibrillation, the use of animplantable cardioverter defibrillator (ICD) system has been shown to bebeneficial. An ICD system includes an ICD, which is a small batterypowered electrical shock device, may include an electrical housing, orcan electrode, that is coupled to one or more implantable medical leadsthat are implanted within the heart. If an arrhythmia is sensed, the ICDmay send a pulse via the implantable leads to shock the heart andrestore its normal rhythm. Owing to the inherent surgical risks inattaching and replacing implantable leads directly within or on theheart, methods have been devised to achieve a similar effect to that ofa transvenous ICD system that is connected directly to the heart withoutplacing implantable leads within the heart or attaching the leadsdirectly to the heart.

Subcutaneous implantable cardioverter-defibrillator (SubQ ICD) systemshave been devised to deliver electrical impulses to the heart by the useof one or more implantable leads that are placed subcutaneously on thetorso. In order to effectively electrically stimulate the heart, thedistal end of the implantable lead may be oriented longitudinallyspanning from approximately the xiphoid to the high sternal area.

Various implantable medical lead structures and methods for positioningand anchoring lead electrodes in proximity to target sites have beendeveloped over the years. New structures and methods are necessary toanchor lead electrodes for emerging therapy delivery requirements.

SUMMARY

Aspects in accordance with principles of the present invention relate toan implantable medical electrical lead for applying electricalstimulation to bodily tissue. The implantable lead is adapted to beintroduced through an access point adjacent to the sternum and a distalportion is navigated into the substernal space. With this in mind, theimplantable lead includes a lead body and an anchoring assembly. Thelead body has a proximal section adapted to be electronically coupled toa power source and a distal section forming at least one exposedelectrode surface.

In accordance with embodiments of the disclosure, the anchoring assemblymay be located along a length of the lead body that is configured to belocated within the substernal space, such as at or near the distal leadend. In other embodiments, the anchoring assembly may be located along alength of the lead body that is configured to be located at or near theaccess point into the substernal space.

Other aspects of the disclosure relate to a method of anchoring animplantable lead system. The method comprises subcutaneously advancingthe lead to an access point into a substernal space of a patient,navigating a distal end of the lead to an implantation site within thesubsternal space, placing the distal end of the lead within thesubsternal space, orienting a fixation element in a pre-determineddirection relative to the substernal space, and fixedly-securing asegment of the lead at the access point with a fixation element thatsecures the lead at an intersection between the subcutaneous space andthe substernal space.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings are illustrative of particular embodiments of theinvention and therefore do not limit the scope of the invention, but arepresented to assist in providing a proper understanding. The drawingsare not to scale (unless so stated) and are intended for use inconjunction with the explanations in the following detailed description.The present invention will hereinafter be described in conjunction withthe appended drawings, wherein like numerals denote like elements, and:

FIG. 1A is a front view of a patient implanted with implantable cardiacsystem;

FIG. 1B is a side view the patient implanted with implantable cardiacsystem 10;

FIG. 1C is a transverse view of the patient implanted with implantablecardiac system;

FIG. 2 depicts an embodiment of a lead anchoring mechanism of a lead ofthe implantable cardiac system;

FIG. 3 depicts an embodiment of a lead anchoring mechanism of a lead ofthe implantable cardiac system;

FIG. 4 depicts an embodiment of a lead anchoring mechanism of a lead ofthe implantable cardiac system;

FIG. 5 depicts an embodiment of a lead anchoring mechanism of a lead ofthe implantable cardiac system;

FIG. 6 depicts an embodiment of a lead anchoring mechanism of a lead ofthe implantable cardiac system; and

FIG. 7 is a flow diagram illustrating an exemplary method of implantinga lead according to an embodiment.

DETAILED DESCRIPTION

The disclosure describes techniques, components, assemblies, and methodsfor anchoring a lead in a patient's substernal space orextra-pericardium, with the lead being attachable to a subcutaneouslyimplanted medical device. A distal end of the lead is positioned at atarget implant site and anchored therein.

In this disclosure, “substernal space” refers to the region defined bythe undersurface between the sternum and the body cavity, but notincluding the pericardium. In other words, the region is posterior tothe sternum and anterior to the ascending aorta. The substernal spacemay alternatively be referred to by the terms “retrosternal space” or“mediastinum” or “infrasternal” as is known to those skilled in the artand includes the region referred to as the anterior mediastinum. Thesubsternal space may also include the anatomical region described inBaudoin, Y. P., et al., entitled “The superior epigastric artery doesnot pass through Larrey's space (trigonum sternocostale).”Surg.Radiol.Anat. 25.3-4 (2003): 259-62 as Larrey's space. For ease ofdescription, the term substernal space will be used in this disclosure,it being understood that the term is interchangeable with any of theother aforementioned terms.

In this disclosure, the term “extra-pericardial” space refers to regionaround the outer heart surface, but not within the pericardialsac/space. The region defined as the extra-pericardial space includesthe gap, tissue, bone, or other anatomical features around the perimeterof, and adjacent to the pericardium.

In this specification, “anchor” means to fix a position of an objectrelative to tissue to minimize movement of the object relative to thetissue. Thus, although there may be small movements of the objectrelative to the tissue, arising for example from body movements of thepatient that give rise to small deflections of the object within thetissue, the object is nevertheless “anchored” in the tissue. It is to beunderstood that features of the various exemplary embodiments describedherein may be combined with each other, unless specifically notedotherwise.

FIGS. 1A-C are conceptual diagrams of a patient 12 implanted with anexample implantable cardiac system 10. FIG. 1A is a front view ofpatient 12 implanted with implantable cardiac system 10. FIG. 1B is aside view patient 12 with implantable cardiac system 10. FIG. 1C is atransverse view of patient 12 with implantable cardiac system 10.

Implantable cardiac system 10 includes an implantable cardiacdefibrillator (ICD) 14 connected to a first lead 16 and a second lead18. The first lead 16 and the second lead 18 may be utilized to providean electrical stimulation therapy such as pacing or defibrillation. Forexample, lead 16 may provide defibrillation therapy while lead 18 mayprovide pacing therapy, or vice versa, while in other embodiments, bothlead 16 and lead 18 may provide pacing therapy or defibrillationtherapy. In the example illustrated in FIGS. 1A-C ICD 14 is implantedsubcutaneously on the left midaxillary of patient 12. ICD 14 may,however, be implanted at other subcutaneous locations on patient 12 asdescribed later.

Lead 16 includes a proximal end that is connected to ICD 14 and a distalend that includes one or more electrodes. Lead 16 extends subcutaneouslyfrom ICD 14 toward xiphoid process 20. At a location near xiphoidprocess 20, lead 16 bends or turns and extends subcutaneously superior,substantially parallel to sternum 22. The distal end of lead 16 may bepositioned near the second or third rib. However, the distal end of lead16 may be positioned further superior or inferior depending on thelocation of ICD 14 and other factors. Although illustrated as beingoffset laterally from and extending substantially parallel to sternum 22in the example of FIGS. 1A-C, lead 16 may be implanted over sternum 22,offset from sternum 22, but not parallel to sternum 22 (e.g., angledlateral from sternum 22 at either the proximal or distal end).

Lead 16 includes a defibrillation electrode 24, which may include anelongated coil electrode or a ribbon electrode, toward the distal end oflead 16. Lead 16 is placed such that a therapy vector betweendefibrillation electrode 24 and a housing or can electrode of ICD 14 issubstantially across the ventricle of heart 26.

Lead 16 may also include one or more sensing electrodes, such as sensingelectrodes 28 and 30, located toward the distal end of lead 16. In theexample illustrated in FIGS. 1A-C, sensing electrode 28 and 30 areseparated from one another by defibrillation electrode 24. ICD 14 maysense electrical activity of heart 26 via a combination of sensingvectors that include combinations of electrodes 28 and 30 and thehousing or can electrode of ICD 14. For example, ICD 14 may obtainelectrical signals sensed using a sensing vector between electrodes 28and 30, obtain electrical signals sensed using a sensing vector betweenelectrode 28 and the conductive housing or can electrode of ICD 14,obtain electrical signals sensed using a sensing vector betweenelectrode 30 and the conductive housing or can electrode of ICD 14, or acombination thereof. In some instances, ICD 14 may even sense cardiacelectrical signals using a sensing vector that includes defibrillationelectrode 24.

Lead 18 includes a proximal end that is connected to ICD 14 and a distalend that includes one or more electrodes. Lead 18 extends subcutaneouslyfrom ICD 14 toward xiphoid process 20. At a location near xiphoidprocess 20 lead 18 bends or turns and extends superior upward in thesubsternal space. In one example, lead 18 may be placed in themediastinum 36 and, more particularly, in the anterior mediastinum. Theanterior mediastinum is bounded laterally by pleurae 40, posteriorly bypericardium 38, and anteriorly by sternum 22. Lead 18 may be implantedwithin the mediastinum such that one or more electrodes 32 and 34 arelocated over a cardiac silhouette of the ventricle as observed viafluoroscopy. In the example illustrated in FIGS. 1A-C, lead 18 islocated substantially centered under sternum 22. In other instances,however, lead 18 may be implanted such that it is offset laterally fromthe center of sternum 22. Although described herein as being implantedin the substernal space, the mediastinum, or the anterior mediastinum,lead 18 may be implanted in other extra-pericardial locations.

Lead 18 includes electrodes 32 and 34 located near a distal end of lead18. Electrodes 32 and 34 may comprise ring electrodes, hemisphericalelectrodes, coil electrodes, helical electrodes, ribbon electrodes, orother types of electrodes, or combination thereof. Electrodes 32 and 34may be the same type of electrodes or different types of electrodes. Inthe example illustrated in FIGS. 1A-C electrode 32 is a hemisphericalelectrode and electrode 34 is a ring or coil electrode.

ICD 14 may deliver pacing pulses to heart 26 via a pacing or therapyvector that includes any combination of one or both of electrodes 32 and34 and a housing electrode or can electrode of ICD 14. For example, ICD14 may deliver pacing pulses using a pacing or therapy vector betweenelectrodes 32 and 34, deliver pacing pulses using a pacing or therapyvector between electrodes 32 and the conductive housing or can electrodeof ICD 14, deliver pacing pulses using a pacing or therapy vectorbetween electrodes 34 and the conductive housing or can electrode of ICD14, or a combination thereof. In some instances, ICD 14 may deliverpacing therapy via a therapy vector between one of electrode 32 (orelectrode 34) and defibrillation electrode 24. In still furtherinstances, ICD 14 may deliver pacing therapy via a therapy vectorbetween one of electrode 32 (or electrode 34) and one of sensingelectrodes 28 or 30. ICD 14 may generate and deliver the pacing pulsesto provide anti-tachycardia pacing (ATP), bradycardia pacing, post shockpacing, or other pacing therapies or combination of pacing therapies. Inthis manner, ATP therapy or post shock pacing (or other pacing therapy)may be provided in an ICD system without entering the vasculature or thepericardial space, nor making intimate contact with the heart.

ICD 14 may generate and deliver pacing pulses with any of a number ofamplitudes and pulse widths to capture heart 26. The pacing thresholdsof heart 26 when delivering pacing pulses substernally using lead 18 maydepend upon a number of factors, including location of electrodes 32 and34, location of ICD 14, physical abnormalities of heart 26 (e.g.,pericardial adhesions), or other factors. The pacing thresholds neededto capture heart 26 tend to increase with shorter pulse widths. In thecase of ATP, ICD 14 may deliver pacing pulses having longer pulse widthsthan conventional ATP pulses to reduce the amplitude of the pacingpulses. For example, ICD 14 may be configured to deliver pacing pulseshaving pulse widths or durations of greater than or equal to one (1)millisecond. In another example, ICD 14 may be configured to deliverpacing pulses having pulse widths or durations of greater than or equalto ten (10) milliseconds. In a further example, ICD 14 may be configuredto deliver pacing pulses having pulse widths or durations of greaterthan or equal to fifteen (15) milliseconds. In yet another example, ICD14 may be configured to deliver pacing pulses having pulse widths ordurations of greater than or equal to twenty (20) milliseconds.Depending on the pulse widths, ICD 14 may be configured to deliverpacing pulses having pulse amplitudes less than or equal to twenty (20)volts, deliver pacing pulses having pulse amplitudes less than or equalto ten (10) volts, deliver pacing pulses having pulse amplitudes lessthan or equal to five (5) volts, deliver pacing pulses having pulseamplitudes less than or equal to two and one-half (2.5) volts, deliverpacing pulses having pulse amplitudes less than or equal to one (1)volt. Typically the lower amplitudes require longer pacing widths asillustrated in the experimental results. Reducing the amplitude ofpacing pulses delivered by ICD 14 reduces the likelihood of extracardiacstimulation.

ICD 14 may sense electrical activity of heart 26 via a combination ofsensing vectors that include combinations of electrodes 32 and 34 andthe housing or can electrode of ICD 14. For example, ICD 14 may obtainelectrical signals sensed using a sensing vector between electrodes 32and 34, obtain electrical signals sensed using a sensing vector betweenelectrode 32 and the conductive housing or can electrode of ICD 14,obtain electrical signals sensed using a sensing vector betweenelectrode 34 and the conductive housing or can electrode of ICD 14, or acombination thereof. In some instances, ICD 14 may sense electricalactivity of heart 26 via a sensing vector between one of electrode 32(or electrode 34) and electrodes 24, 28 and 30 of lead 16. ICD 14 maydeliver the pacing therapy as a function of the electrical signalssensed via the one or more of the sensing vectors of lead 18.Alternatively or additionally, ICD 14 may deliver the pacing therapy asa function of the electrical signals sensed via one or more of thesensing vectors of lead 16.

ICD 14 also analyzes the sensed electrical signals from one or more ofthe sensing vectors of lead 18 and/or one or more of the sensing vectorsof lead 16 to detect tachycardia, such as ventricular tachycardia orventricular fibrillation. In some instances, ICD 14 delivers one or moreATP therapies via the one or more pacing or therapy vectors of lead 18in response to detecting the tachycardia in an attempt to terminate thetachycardia without delivering a defibrillation shock. If the one ormore ATP therapies are not successful or it is determined that ATPtherapy is not desired, ICD 14 may deliver one or more defibrillationshocks via defibrillation electrode 24 of lead 16.

The configuration described above in FIGS. 1A-1C is directed toproviding ventricular pacing via lead 18. In situations in which atrialpacing is desired in addition to or instead of ventricular pacing, lead18 may be positioned further superior. A pacing lead configured todeliver pacing pulses to both the atrium and ventricle may have moreelectrodes. For example, the pacing lead may have one or more electrodeslocated over a cardiac silhouette of the atrium as observed viafluoroscopy and one or more electrodes located over a cardiac silhouetteof the ventricle as observed via fluoroscopy. A pacing lead configuredto deliver pacing pulses to only the atrium may, for example, have oneor more electrodes located over a cardiac silhouette of the atrium asobserved via fluoroscopy. In some instances, two substernal pacing leadsmay be utilized with one being an atrial pacing lead implanted such thatthe electrodes are located over a cardiac silhouette of the atrium asobserved via fluoroscopy and the other being a ventricle pacing leadbeing implanted such that the electrodes are located over a cardiacsilhouette of the ventricle as observed via fluoroscopy.

ICD 14 may include a housing that forms a hermetic seal that protectscomponents of ICD 14. The housing of ICD 14 may be formed of aconductive material, such as titanium. ICD 14 may also include aconnector assembly (also referred to as a connector block or header)that includes electrical feedthroughs through which electricalconnections are made between conductors within leads 16 and 18 andelectronic components included within the housing. As will be describedin further detail herein, housing may house one or more processors,memories, transmitters, receivers, sensors, sensing circuitry, therapycircuitry and other appropriate components. Housing 34 is configured tobe implanted in a patient, such as patient 12.

Leads 16 and 18 include a lead body that includes one or more electrodeslocated near the distal lead end or elsewhere along the length of thelead body. The lead bodies of leads 16 and 18 also contain one or moreelongated electrical conductors (not illustrated) that extend throughthe lead body from the connector assembly of ICD 14 provided at aproximal lead end to one or more electrodes of leads 16 and 18. The leadbodies of leads 16 and 18 may be formed from a non-conductive material,including silicone, polyurethane, fluoropolymers, mixtures thereof, andother appropriate materials, and shaped to form one or more lumenswithin which the one or more conductors extend. However, the techniquesare not limited to such constructions.

The one or more elongated electrical conductors contained within thelead bodies of leads 16 and 18 may engage with respective ones ofelectrodes 24, 28, 30, 32, and 34. In one example, each of electrodes24, 28, 30, 32, and 34 is electrically coupled to a respective conductorwithin its associated lead body. The respective conductors mayelectrically couple to circuitry, such as a therapy module or a sensingmodule, of ICD 14 via connections in connector assembly, includingassociated feedthroughs. The electrical conductors transmit therapy froma therapy module within ICD 14 to one or more of electrodes 24, 28, 30,32, and 34 and transmit sensed electrical signals from one or more ofelectrodes 24, 28, 30, 32, and 34 to the sensing module within ICD 14.

The lead 18 further includes one or more anchoring mechanisms that arepositioned along the length of the lead body. The anchoring mechanismsaffix the lead 18 that is implanted in a substernal space in a fixedlocation to prevent dislodging of the lead 18 once it is implanted. Forexample, the lead 18 may be anchored at one or more locations situatedbetween the distal lead end positioned within the substernal space ofpatient 12 and a point along the length of the portion of the lead bodyat or near the insertion point of the lead body into the substernalspace. The one or more anchoring mechanism(s) may either engagecartilage, bone, fascia, muscle or other tissue of patient 12 or maysimply be wedged therein to affix the lead under the sternum to preventexcessive motion or dislodgment. Furthermore, it should be understoodthat various anchoring mechanisms described in this disclosure mayadditionally be utilized for delivery of a stimulation therapy as isknown in the art.

In accordance with various embodiments, this disclosure describesanchoring mechanisms that are integrated into the lead body. In suchembodiments, a portion or segment of the lead body may be formed withmaterials that function to encase conductors and other elements internalto the lead while also anchoring the lead within the implantenvironment.

In alternative embodiments, anchoring mechanisms of the disclosure aredescribed as discrete elements that may be formed in line with the leadbody. In some embodiments, the discrete components may be provided in afixedly-secured relationship to the lead body. In other embodiments, theanchoring mechanism may be detachedly coupled in a sliding relationshipover the lead body.

The anchoring mechanisms may include a passive anchoring mechanism, anactive anchoring mechanism or a combination of both. In one embodiment,the anchoring mechanism is coupled along a length of the lead body andit may also function as an electrically active element. Examples ofpassive anchoring mechanisms include flanges, disks, pliant tines,flaps, porous structures such as a mesh-like element that facilitatestissue growth for engagement, bio-adhesive surfaces (such as thosedescribed in U.S. Pat. No.: 8,594,809, which is incorporated herein byreference in its entirety), and/or any other non-piercing elements.Examples of active anchoring mechanisms may include rigid tines, prongs,burbs, clips, screws, and/or other projecting elements that pierce andpenetrate into tissue to anchor the lead. As another example of anactive anchoring mechanism, the lead may be provided with a side helixfor engaging tissue. It is contemplated that any of these anchoringmechanisms will be formed from materials including shape memory alloyssuch as Nitinol to facilitate the deployment of the lead.

The various examples of the anchoring mechanisms may be deployable. Assuch, the anchoring mechanism assumes a first state during maneuveringof the lead (during which time the lead is disposed within a lumen of adelivery system or over a guidewire or stylet) to the desired implantlocation. Subsequently, the anchoring mechanism assumes a second statefollowing the release of the lead from the delivery system into thesubsternal space to thereby anchor the distal end portion of the leadbody relative to the adjacent tissue.

In addition or alternatively, the lead may be anchored through a suturethat fixedly-secures the lead to the cartilage, musculature, tissue orbone at the access point into the substernal space of patient 12. Insome embodiments, the suture may be sewn to the patient 12 throughpre-formed suture holes to the patient 12.

As shown in FIG. 1A, an anchoring mechanism 50 a or anchoring mechanism50 b (collectively “anchoring mechanism 50”) may be provided along thelead body to couple the lead 18 at an access point through which thedistal end of the lead 18 is inserted into the substernal space. Theaccess point is any location that provides access into the substernalspace. In one exemplary embodiment, the access point is adjacent to orbelow the xiphoid process (also referred to as “subxiphoid”). The accesspoint may also be at the notch (not shown) that connects the xiphoidprocess to the sternum. In other embodiments, the substernal space mayalso be accessed through the manubrium.

An example of the anchoring mechanism 50 a includes a suture or clip orother fastener that anchors the lead body to the patient 12. Theanchoring mechanism 50 a embodied as a fastener may be coupled directlyto the lead body or to a suture sleeve such as that described in U.S.Pat. No. 5,273,053, issued to Pohndorf and incorporated herein byreference in its entirety. The anchoring mechanism 50 a isfixedly-coupled to cartilage, musculature, tissue or bone at the entrypoint into the substernal space at or near the access point at whichsite the body of the lead 18 transitions from the subcutaneous tissueinto the substernal space of patient 12.

In an embodiment, the anchoring mechanism 50 a that is positioned at theaccess point may further be formed to accommodate the curvature of thepatient 12 anatomy. In other words, the body of the anchoring mechanism50 a embodied, for example as a suture sleeve, may be malleable orpre-shaped to conform to the bend angle of the site at which the lead 18transitions from the subcutaneous tissue into the substernal space ofpatient 12. As such, the suture sleeve may include a segment having apreformed bend angle of approximately 90 degrees. Thus, the anchoringsleeve may be positioned partially in the subcutaneous tissue andpartially within the substernal space. The anchoring sleeve may becoupled to the patient 12 at one or more points along the length of theanchoring sleeve.

The anchoring mechanism 50 a may further be constructed to facilitatetissue in-growth for long-term fixation of the lead 18. To promote suchtissue in-growth, the anchoring mechanism 50 a may be formed having amulti-layer construction or having pores. In some embodiments, theanchoring mechanism 50 a may be constructed having a cross-linkedstructure. In accordance with other embodiments, the materials forconstruction of the anchoring mechanism 50 a having a multi-layerstructure may include bio-absorbable materials which will degrade ashort time after implant. The anchoring mechanism 50 a may also includea collagen layer which has been pre-treated to promote the tissuegrowth.

An example of the anchoring mechanism 50 b may include a fixationelement that is disposed continuously or partially around the body oflead 18 to couple the lead 18 to the access point. The anchoringmechanism may be fixedly coupled to the lead or slidingly-disposed overthe lead, such as the anchoring member described in U.S. Pat. No.5,476,493 to Muff, which is configured to be movable axially along thelength of the lead body, to facilitate positioning of the anchoringmechanism 50 b at a point suitable for affixation to tissue adjacent tothe xiphoid process. In other words, anchoring mechanism 50 b may bedisposed around the lead body in a sliding relationship to facilitatenavigation and placement of the distal end of the lead into thesubsternal space and the subsequent movement of the anchoring mechanism50 b to the site for fixation.

In some embodiments, lead 18 further includes a reinforced distal end 36that is formed to facilitate anchoring of the lead 18 within thesubsternal space. The reinforced distal end 36 of the lead 18 preventsflexing of the lead 18 responsive to body motions. The distal end 36 maybe formed from a material having a greater stiffness coefficientrelative to that of the material of the lead body, or with a coating, ora resilient member—such as a coil—coupled over the lead body, any ofwhich is fabricated to impart stiffness to the distal end 36. Thereinforced distal end 36 exhibits characteristics that eliminate orminimize the motion of the distal end of the lead. As such, the distalend 36 functions to anchor the lead 18 within the tissue of patient 12.

In addition, the reinforced distal end 36 may be constructed tofacilitate tissue in-growth for long-term fixation of the lead 18. Topromote such tissue in-growth, the distal end 36 may be formed having amulti-layer construction or having pores. In some embodiments, thedistal end 36 may be constructed having a cross-linked structure. Inaccordance with other embodiments, the materials for construction of thedistal end 36 having a multi-layer structure may include bio-absorbablematerials which will degrade a short time after implant. The distal end36 may also include a collagen layer which has been pre-treated topromote the tissue growth.

A backfilling process may be utilized to increase the stiffnesscoefficient of the reinforced distal end 36 relative other segments ofthe body of lead 18. For example, the lead 18 body may be formed withmultiple insulative layers with the backfill material—such as a medicaladhesive or additional material—being added to reinforce the distal end36. In other embodiments, the reinforced distal end 36 may be formedwith materials having an increased rigidity, relative to the rest of thelead body. For example, the reinforced distal end 36 may be fabricatedfrom such materials as an ultra-high molecular density polyethylene,polyester or other high tensile strength fiber or plastic. In otherexamples, a lead body of lead 18 that is manufactured of relatively softplastics of low tensile strength may be reinforced to provide areinforced distal end 36 by increasing the layers of material used inthe region of distal end 36.

The examples illustrated in FIGS. 1A-C are exemplary in nature andshould not be considered limiting of the techniques described in thisdisclosure. In other examples, ICD 14, lead 16, and lead 18 may beimplanted at other locations. For example, ICD 14 may be implanted in asubcutaneous pocket in the right chest. In this example, lead 16 may beextend subcutaneously from the device toward the manubrium of thesternum and bend or turn and extend subcutaneously inferiorly from themanubrium of the sternum, substantially parallel with the sternum andlead 18 may extend subcutaneously from the device toward the manubriumof the sternum to the desired location and bend or turn and extendsubsternally inferiorly from the manubrium of the sternum to the desiredlocation.

In the example illustrated in FIG. 1, system 10 is an ICD system thatprovides pacing therapy. However, these techniques may be applicable toother cardiac systems, including cardiac resynchronization therapydefibrillator (CRT-D) systems, cardioverter systems, or combinationsthereof.

In addition, it should be noted that system 10 may not be limited totreatment of a human patient. In alternative examples, system 10 may beimplemented in non-human patients, e.g., primates, canines, equines,pigs, bovines, ovines, and felines. These other animals may undergoclinical or research therapies that may benefit from the subject matterof this disclosure.

FIG. 2 depicts a lead anchoring mechanism 60 that includes a pluralityof struts 62 that are disposed over the lead 18 in a slidingrelationship and are configured to expand from a collapsed configurationto an expanded configuration such that the plurality of struts 62 expandto press against tissue surrounding the implant location.

In one embodiment, the struts 62 may be displaced distally—relative to amid-axis of the lead 18—by employing a deployment member (not shown)that causes both distal-ward movement and expansive displacement of thestruts 62 into the expanded state. Other deployment mechanisms mayinclude pneumatic activation (fluid or gas activated), or directconnection via rods, or any other type of proximally applied torque thatcauses force transfer to deploy the struts 62.

According to one exemplary embodiment, the lead anchoring mechanism 60is made from a super-elastic material. The struts 62 may be formed froma tubular collar with material being removed to form two or moreexpandable struts 62.

The lead 18 in FIG. 2 further includes a canted distal portion 64. Asillustrated, the body of lead 18 is pre-shaped to be canted at an anglein the range of 10 degrees to 90 degrees, relative to the remaining,proximal, portion of the lead body. The pre-shape canted distal portion64 may be constructed by providing an inner layer having a shape memorymaterial over this section of the lead body. During delivery of the leadbody, the lead 18 may be positioned with a catheter or other deliverysystem that causes the canted distal portion 64 to be straightened.Therefore, the bias of the distal portion 64 is such that theintroduction of a straight stylet into a center lumen of the lead bodyor the insertion of lead body into a guide catheter may cause the bendto be straightened. Upon insertion into the substernal space, the canteddistal portion 64 permits the lead body to assume the pre-determinedshape thereby causing the distal portion 64 to anchor to tissue withinthe substernal space.

Although the canted distal portion 64 is shown in conjunction with theanchoring mechanism 60, it should be noted that alternative embodimentsof the lead 18 may simply include the canted distal portion 64 withoutthe anchoring mechanism 60.

In FIG. 3, an anchoring mechanism 70 is coupled to the distal end of thelead 18. The anchoring mechanism 70 may be configured as a flange or padmounted to the distal end of the lead 18. The anchoring mechanism 70includes a major surface 72 that is greater than a minor surface (notshown) that is perpendicular to the major surface. The major surface 72is characterized by a width that is greater relative to the width of theminor surface. When coupled to the lead 18, the major surface isoriented in line with an imaginary axis of the body of lead 18 runningcontinuously between the proximal end and the distal end. Thecross-sectional profile of the anchoring mechanism 70 is dimensioned tobe greater than a cross-sectional profile of the lead 18. For example,the anchoring mechanism 70 may be configured having a width that isgreater than that of the lead 18 as viewed from a side perspective orside cross-section.

Electrode 32 may be attached to the lead 18 overlying a portion of leadanchoring mechanism 70. In this mounting configuration, the electrode 32may be oriented to direct the field of the stimulation energy in apre-determined direction at the implant location.

In one embodiment, anchoring mechanism 70 may include a mesh-likestructure having pores that permit ingrowth of tissue that affixes tothe anchoring mechanism. In other embodiments, the anchoring mechanism70 may include a bioreactive adhesion layer (not shown) such as thatdescribed in the U.S. Patent Application No. 2009/0270962, with thebioreactive adhesion layer being coupled to the surface of the anchoringmechanism 70. In such an embodiment, a cover (not shown) may be utilizedto seal off the bioreactive adhesion layer from the external environmentuntil the anchoring mechanism is situated at an appropriate implantsite.

FIG. 4 illustrates an anchoring mechanism 80 having a combinationpassive fixation element 82 and an active fixation element 84 coupled tothe distal end of lead 18. The illustration depicts the fixation element82 and fixation element 84 in an expanded or deployed configuration. Thepassive fixation element 82 may be a disk that expands radially relativeto the width of the lead body to define a circumference that is largerthan the circumference of the lead body. The anchoring mechanism 80further illustrates active fixation element 84 that may be a helix thatextends in axially from the distal end of the lead body and isconfigured for insertion into tissue. The fixation element 84 may bescrewed out of the distal tip of the lead body, for example, through arotational force that is imparted by rotating the lead body.

FIG. 5 illustrates an anchoring mechanism 90 coupled along a length ofthe lead body. The anchoring mechanism 90 comprises a side helix thatengages with tissue. The side helix may be formed as a coil wound overthe lead body. Engagement of the tissue occurs through protrusion of theside helix in a direction that is perpendicular to an imaginary axisfrom the proximal to the distal end of the lead.

FIG. 6 is a side view of anchoring mechanism 100 positioned at aproximal end of electrode 32 of a lead of a medical device according toan embodiment. The anchoring mechanism 100 is positioned proximal fromthe electrode 32 on the lead body of lead 18 and includes proximal tinesthat are formed of flexible or pliant material such as polymericmaterials for example, as silicone rubber or polyurethane to passivelyfixate to tissue. In another embodiment, the tines may be formed of arigid material such as titanium or PEEK for active fixation to thetissue. During deployment of the anchoring mechanism 100, the tines arefolded such that the tine elements are retracted or constrained againstthe lead body. This may be accomplished by positioning the lead 18within a lumen of a delivery system having a diameter smaller than thewidth defined by the expanded tines. Upon delivery to the properlocation, the lead 18 is released from the delivery system allowing thetines to return to their extended position whereby they push against orpierce the tissue improving both acute and chronic fixation.

FIG. 7 is a flow diagram illustrating an exemplary method of implantinga lead according to an embodiment of the disclosure. In particular, themethod involves implantation of a medical lead in a substernal spaceunderneath the sternum and fixedly-securing the distal end of the leadto patient tissue. Lead 18

(FIGS. 1-6) comprises one example of such a medical lead that may beimplanted in the substernal space.

The lead 18 is implanted in a region that is underneath the sternum andwithin the mediastinum space. The mediastinum space may include theregion that is posterior to the sternum and anterior to the pericardialsac from the xiphoid to the manubrium and bounded laterally on the leftand right by the internal thoracic arteries. A lead implanted in thesubsternal space may provide a stimulation therapy, such as a pacingtherapy (including anti-tachy pacing, post-shock pacing, chronic pacing)or a defibrillation therapy or both.

A delivery system such as that disclosed in U.S. Patent Application No.:61/820,014, “Systems And Methods For Implanting A Medical ElectricalLead Within A Substernal Space” which is hereby incorporated byreference in its entirety, may be utilized to implant the lead. Whenused, the delivery system is navigated into the substernal space throughan access point on the patient (202). The navigation of the deliverysystem to the appropriate location may be aided by various navigationaids discussed in the 61/820,014 application, including: a radiopaquemarker that is visualized through fluoroscopy, signals obtained from thedistal end of the delivery system body, and a directional indicator onthe delivery system. Again, the access point may be any location on thetissue of the patient 12 where an incision is made to provide accessinto the substernal space.

At task 204, a distal end of the lead is navigated to the implantationsite within the substernal space. The lead body may extend from astimulation therapy generating device, such as device 14, that ispositioned subcutaneously, such as at the left mid-axillary of thepatient, and tunneled toward the xiphoid process. The navigation of thelead from the xiphoid process into the substernal space may be performedsuch that the distal end of the lead is directed toward the jugularnotch from the xiphoid process in a generally axial direction.

The distal end of the lead is positioned within the substernal space ata location over a cardiac silhouette of the ventricle as observed viafluoroscopy. In particular, the electrodes may be oriented towards atarget stimulation site (206). In one example, the desired orientationof the electrode may be achieved by orienting an anchoring mechanismthat is coupled to the lead in a direction that causes the electrode tobe positioned in a direction towards the target stimulation site. Forexample, the electrode may be formed integrally with an anchoringmechanism such as that described in FIG. 3. In this configuration, themovement, including rotational or longitudinal movement, of theanchoring mechanism triggers movement of the electrode in thecorresponding direction which facilitates orientation of the electrodein the desired direction.

At task 208, the lead is anchored to tissue surrounding the implantenvironment. The lead may be anchored at the distal end, proximate tothe distal end or any other location along the length of the leadbetween the access point into the xiphoid process and the distal end ofthe lead. In doing so, the portion of the lead within the substernalspace is anchored to prevent dislodgment of the lead.

In some embodiments, the anchoring mechanism may be configured in afirst retracted configuration during the navigation of the lead andre-configured into a second expanded configuration when the lead isreleased within the substernal space. In other embodiments, theanchoring mechanism is retracted from an interior portion of the lead.Additionally, the lead body may be sutured at or near the xiphoidprocess to fixedly couple the lead.

At task 210, the delivery system is retracted from the patient after thelead has been guided to the implant site.

As described herein, anchoring devices, systems and methods inaccordance with various embodiments are provided that facilitateimplantation and stabilization of a lead in the substernal space. Inalternative implementations, the devices, systems and methods may beutilized for lead implantation and fixation in locations other than thesubsternal space including but not limited to the aforementionedextra-pericardial space.

Various examples have been described. It is contemplated that thefeatures described in the different embodiments may be combined tocreate additional embodiments. All such disclosed and other examples arewithin the scope of the following claims.

What is claimed is:
 1. An implantable medical system comprising: astimulation therapy generator; a first elongate lead coupled to thestimulation therapy generator having a proximal end and a distal end; anelectrode coupled to the distal end of the first elongate lead; and ananchoring mechanism disposed along a length of the first elongate leadconfigured to fixedly-secure the first elongate lead within a substernalspace underneath the sternum.
 2. The implantable medical system of claim1, wherein the anchoring mechanism comprises a reinforcement membercoupled to the distal end of the lead that is configured to preventmovement of the lead responsive to a dislodgment force from the tissueat the implant location.
 3. The implantable medical system of claim 1,wherein the anchoring mechanism comprises a canted distal portion formedat the distal end of the lead such that the canted distal portionengages tissue within the substernal space to anchor the lead.
 4. Theimplantable medical system of claim 1, wherein the anchoring mechanismcomprises a distal section of the lead that is configured having amaterial that includes a greater stiffness coefficient relative to theproximal section of the lead.
 5. The implantable medical system of claim1, wherein the anchoring mechanism is configured to position theelectrode in a pre-determined orientation relative to a targetstimulation therapy site that is not within the substernal space.
 6. Theimplantable medical system of claim 1, wherein the anchoring mechanismcomprises a flange having at least one major surface that is oriented ina parallel configuration with a length of the lead.
 7. The implantablemedical system of claim 1, wherein the anchoring mechanism is configuredto fixedly-secure the first elongate lead at an access point into thesubsternal space, wherein a distal end of the lead is configured to betunneled through a pathway across subcutaneous tissue for insertion intothe substernal space.
 8. The implantable medical system of claim 1,wherein the anchoring mechanism includes a porous structure disposed atthe distal end of the lead.
 9. The implantable medical system of claim8, wherein the anchoring mechanism comprises an in-growth member havinga substance configured to promote tissue growth for anchoring theimplantable stimulation lead to tissue.
 10. The implantable medicalsystem of claim 1, wherein the anchoring mechanism is slidingly-disposedalong a length of a body of the first elongate lead, and wherein theanchoring mechanism is moveable along the length of the body duringnavigation of the lead.
 11. The implantable medical system of claim 1,wherein the anchoring mechanism comprises a passive fixator disposedalong a length of a body of the first elongate lead and configured toengage tissue.
 12. The implantable medical system of claim 1, whereinthe anchoring mechanism comprises an active fixator disposed along alength of a body of the first elongate lead and configured to engagetissue.
 13. The implantable medical system of claim 1, wherein theanchoring mechanism comprises an expandable coil.
 14. The implantablemedical system of claim 1, wherein the anchoring mechanism comprises anexpandable porous structure having pores for tissue engagement.
 15. Theimplantable medical system of claim 1, wherein the first elongate leadand the anchoring mechanism are configured for deployment into thesubsternal space through a delivery system such that the anchoringmechanism remains in the first constrained configuration during deliveryof the lead to the substernal space and is released to the secondexpanded configuration subsequent to release of the lead into thesubsternal space.
 16. The implantable medical system of claim 1, furthercomprising a second elongate lead coupled to the stimulation therapygenerator and wherein the second elongate is configured for implantationat a subcutaneous implant location.
 17. A method of implanting a medicalsystem, comprising: subcutaneously advancing a first lead through asubcutaneous space from a subcutaneously positioned implantable medicaldevice to an access point into a substernal space; navigating a distalend of the first lead to an implantation site within the substernalspace; placing the distal end of the first lead within the substernalspace; orienting a fixation element in a pre-determined directionrelative to the substernal space; and fixedly-securing a segment of thefirst lead at the access point with a fixation element that secures thelead at an intersection between the subcutaneous space and thesubsternal space.
 18. The method of implanting the medical system ofclaim 17, wherein the orientation of the fixation element is configuredto conform to curvature of a transition from the subcutaneous tissueinto the substernal space.
 19. The method of implanting the medicalsystem of claim 17, further comprising performing an incision at axiphoid process of a patient to create the access point into substernalspace.
 20. The method of implanting the medical system of claim 17,further comprising anchoring the distal end of the first lead to thetissue.
 21. The method of implanting the medical system of claim 20,wherein the anchoring comprises suturing the distal end to the tissue.22. The method of implanting the medical system of claim 20, wherein theanchoring comprises deploying a fixation element for coupling with thetissue.
 23. The method of implanting the medical system of claim 22,wherein the fixation element is selected from the group consisting of aprong, burb, clip, screw, flange, disk, flap, and a porous structure.24. The method of implanting the medical system of claim 20, wherein theanchoring comprises deploying an anchoring mechanism oriented in a firstretracted configuration into the substernal space such that the deployedanchoring mechanism is oriented in a second expanded configuration whenpositioned in the substernal space.
 25. The method of implanting themedical system of claim 20, wherein the orientation of the anchoringmechanism triggers a corresponding orientation of an electrode of thefirst lead towards a target stimulation therapy site.
 26. The method ofimplanting the medical system of claim 20, wherein the anchoringmechanism is configured in a first retracted configuration during thenavigation of the lead and configured into a second expandedconfiguration when the lead is placed within the substernal space. 27.The method of implanting the medical system of claim 17, whereinnavigating the first lead comprises: inserting the first lead into adelivery system having a distal end portion that is positioned withinthe substernal space, wherein the distal end of the delivery systemcomprises a sheath having a lumen into which the first lead is disposed;advancing the distal end of the first lead towards the distal endportion of the delivery system; and retracting the delivery system overthe first lead from the substernal space.
 28. The method of implantingthe medical system of claim 17, further comprising positioning anelectrode disposed on the distal end of the first lead such that a fieldof an electrical stimulation applied through the electrode is directedtoward a stimulation site.
 29. The method of implanting the medicalsystem of claim 17, further comprising subcutaneously advancing a secondlead for fixation in subcutaneous tissue, wherein the first leaddelivers a pacing stimulation therapy and the second lead delivers adefibrillation stimulation therapy.
 30. The method of implanting themedical system of claim 17, wherein the first lead delivers acombination therapy including pacing stimulation and defibrillationstimulation.